These studies concern the neuroendocrine impairments associated with reproductive aging in C57B1/6J mice. The roles of the ovary will be analyzed in two respects: 1. the contribution of the reduced number of ovarian follicles to the early changes in reproductive cycles, and 11. the role of disturbed endocrine regulation in causing hypothalamic-pituitary impairments. Experiments will test the reversibility of age changes by long-term ovariectomy and the intensification of age changes by treatment with estradiol (E2). Neuroendocrine function will be assayed by the LH surge, the performance of ovarian grafts, hypothalamic monoamine metabolism nuclear receptors for E2 in the hypothalamus, and hypothalamic neuronal number. These studies bear on the etiology of pituitary tumors of adult humans (in which disturbances of phyothalamic monoamine metabolism are implicated), on the ovarian role in menopausal dysfunctions, and on possible but yet unidentified effects of chronic steroid usage in humans through contraceptives and postmenopausal therapy.